1. Field of the Invention
The present invention relates to a musical-tone-signal-generating apparatus, and more particularly, to a tone-color-selecting technique for the apparatus.
2. Prior Art
Among conventional electronic organs which can simulate a pipe organ, a type provided with a number of tone-selecting switches called "flute-couplers" is known. Each of these tone-selecting switches, for example, corresponds to one of the following foot-sounds: 1', 2', 4', 5(1/3)', 8', and 16'.
In the above-mentioned electronic organ, a plurality of the tone-selecting switches can be simultaneously turned on, so that a plurality of foot-sounds corresponding to the on-switches can be generated simultaneously. In order to generate a number of foot-sounds, a plurality of musical-tone-generating channels must be provided in a parallel fashion or in a time-sharing fashion. As a result, the number of the musical-tone-generating channels increases with the number of tones simultaneously generated, and consequently, the configuration of the apparatus becomes more complex and cost increases.
To overcome these problems, another technique is proposed (for example, see U.S. Pat. No. 3,823,390). This technique produces musical-tone waveforms to be generated by computation each time a number of tone colors are selected, and the resultant waveforms are stored into wave memories. The computation above is performed on the basis of the volume-level information and the musical-tone-spectrum information corresponding to the selected tone colors. According to the technique, though the number of the wave memories can be reduced, the circuit configuration for computing the waveforms must remain complex.
A similar problem occurs not only in the tone-color selection of the flute-coupler, but also in other tone-color-selections, such as that of a horn, a bass, or the like. For this reason, it was usual that simultaneous selection of two or more tone colors in the same tone group was inhibited, and only one tone color selected by one of the tone-color-selecting switches of each tone group was allowed.